Complete inhibition of char formation from cellulose in fast pyrolysis with aromatic substance

•Slow pyrolysis in aromatic substance is not effective for inhibition of char.•Fast pyrolysis in aromatic substance completely inhibits char formation.•Boiling point >400 °C and polar substituents are required for aromatics.•The major volatile product is levoglucosan and the selectivity increases.•Liquid-phase intermediates play critical roles during fast pyrolysis.

Aromatic substances stabilize levoglucosan and other monomeric glycosides by solvation against thermal decomposition including char formation. We applied this stabilization to inhibit char formation from cellulose, a crystalline polysaccharide. Cellulose was heated with various types of aromatic substances in a heating mantle (slow pyrolysis) or by inserting a sample in a ceramic boat into a furnace preheated to 700 °C under a nitrogen flow (fast pyrolysis). As a result, only fast pyrolysis in aromatic substances with polar substituents (>CO or N) and high boiling points >400 °C completely inhibited the char formation. By the NMR analysis, the major product was identified to be levoglucosan (LG), and the selectivity increased in the presence of aromatic substances probably due to the stabilization of LG in the molten products produced from cellulose fast pyrolysis. The phscicochemical properties required for aromatic substance are discussed with the nature of the cellulose crystallite surface and its decomposition temperature.